1. Field of the Invention
This invention relates to automatic test equipment for testing integrated circuits and other electronic components, and in particular to a method and apparatus for use in such automatic test equipment to enable measurement of the settling time of an analog signal having a varying amplitude.
2. Description of the Prior Art
Automatic test equipment for the testing of integrated circuits and other electronic components is well known. In the testing of components which produce analog signals, it is frequently desirable to measure the settling time of an analog signal having a varying amplitude. Typically such a signal is generated by supplying an appropriate input signal to the device being tested and then detecting the output signal which results. For many electronic components the resulting output signal will be an oscillating waveform which converges on a steady state value. The settling time, or time required for the oscillating waveform to converge to within a specified band around the desired steady state output signal, is often an important characteristic of the circuit or device being tested.
The conventional prior art approach to measure the settling time of the oscillating waveform has been to display the waveform on an oscilloscope where a skilled person watches the signal and estimates the time required for the signal to converge within a desired band around its ultimate value. This approach, of course, suffers from several disadvantages. It is obviously highly dependent upon the care with which the person involved observes the diminishing waveform, is generally expensive, and is subject to frequent errors, particular where high precision is desired.
Another approach has been suggested in "A New Technique for Testing Settling Time in a Production Environment," by J. Whealler, and published as paper 11.4, 1981 IEEE Test Conference at page 312. This paper also describes the importance of accurately measuring settling time, and describes a technique for measuring settling time. Unfortunately, the technique described requires repeatedly testing the part or component, with each test requiring a special set-up procedure. Furthermore the test procedure itself is time consuming, and generally not suited for use in a production environment.